Manufacture of sulphuric acid



July 9, 1940. A. w. WAHLGREN MANUFACTURE OF SULPHURIC ACID Filed Jan. 22, 1938 FORE FEED AND ABSORBERS L L .E R T O C O T S R m n m K N m n K v: R m O R Illlllllllllll III,-

CYCLONE PRECIPJTATOR ATTORNEY .fl/bePf 14/. Warez? INVENTOR Patented July 9, 1940 UNITED STATES PATENT OFFICE 2,207,364 MANUFACTURE or SULPHURIC Aom Application January 22, 1938, Serial No. 186,336

2 Claims.

This invention relates to the manufacture of sulphuric acid by the contact process and more particularly to improvements in the process for producing sulphur dioxide by the combustion of iron sulphide materialscontaining carbonaceous matter.

In the manufacture of sulphuric acid by the contact process sulphur dioxide is commonly produced by the combustion of iron sulphide materials. When iron sulphide materials containing large amounts of carbonaceous material, for example coal brasses, are employed, the large quantities of carbon dioxide produced lower the sulphur dioxide concentration and impair the conversion efiiciency.

It is an object of this invention to avoid this disadvantage and to provide processes for the economic treatment of coal brasses to obtain a higher ratio of sulphur dioxide to carbon dioxide. Further objects will become apparent hereinafter.

The objects of the invention are accomplished by subjecting the coal brasses to dry distillation prior to introduction in the combustion zone, preferably by passing the combustion gases in indirect heat exchange with the coal brasses being fed to the combustion zone. In this manner the volatile carbonaceous matter in the coal brasses is driven ofi, thereby reducing the carbon content of the coal brasses and consequently increasing the sulphur dioxide to carbon dioxide ratio in the combustion gases.

Inasmuch as the heat of the combustion gases is more than adequate for this purpose no substantial increase in the cost of operation is involved. Moreover, such increase in the cost of operation as may be due to maintenance and operation of additional equipment is more than offset by the increased capacity of the roasting equipment and the value of the by-products recovered.

As the capacity of any particular roasting equipment is governed largely by the B. t. u. content of the coal brasses, it will be apparent that a reduction in the carbonaceous content and. the' 45 corresponding reduction in the B. t. u. content duced the capacity of the roasting apparatus, may be recovered for such purposes as may be available.

The treatment of coal brasses prior to combustion according to the processes of this invention is not unlike the dry distillation of coal, and the effluent gases may be treated for the recovery of the various by-products according to the usual procedures in that art. The processes of this invention, however, differ in one essential particular in that simultaneously with the evolution of the volatile matter in the coal brasses considerable amounts of the labile sulphur atom of the iron sulphides is driven 01f as sulphur vapor, a certain amount of which is also reduced to hydrogen sulphide by the hydrocarbons evolved.

The sulphur value of the distillate may be recovered in any suitable manner. Preferably, however, I pass the eflluent gases thru a hot condenser to condense out the sublimed sulphur in a molten state. This permits the other gases to be carried forward for absorption in suitable media or for what other disposition may be desired. The molten sulphur taken olf will then be available for introduction into the combustion zone or for consumption in sulphur burning units. Such hydrogen sulphide as may be contained in the effluent gases may be recovered by suitable absorbents and introduced into the combustion zone if desired.

Alternatively, the sulphur value of the efiluent gases may be recovered by burning the gases leaving the distillation unit to form sulphur dioxide and carbon dioxide and recovering the sul- 35 phur dioxide by a suitable regenerative absorption process.

In the accompanying drawing I have illustrated a typical installation employing a rotary kiln as a combustion chamber. Coal brasses suitably crushed to obtain as large an exposure as possible and tofacilitate combustion are fed into a distillation chamber constructed in much the same manner as the conventional rabble furnace but jacketed with a well insulated chamber thru which the combustion gases are led. The arrangement of rabble arms and shelves illustrated insures adequate exposure for obtaining the desired distillation of volatile matter. The treated coal brasses are then fed into the rotary kiln in the usual manner.

Between the rotary kiln and the distillation chamber is a cyclone precipitator for removing entrained particles. This also serves to cool combustion gases so that overheating in the distillation chamber and excessive evolution of sulphur vapor is avoided. The combustion gases then pass on to the Cottrell precipitators and then to the converters in the usual manner. It further cooling is desired it may be expedient to place the Cottrell precipitators ahead of the distillation chamber.

The effluent gas is led to a hot condenser for the recovery of elemental sulphur in the molten state, as already described, with the other gases passing on to suitable scrubbers or absorbers or being disposed of in such manner as may be desired.

While I have illustrated my invention with reference to particular types of combustion and distillation apparatus, it is to be understood that my invention is not limited in this respect but that other types of roasting apparatus employed for the production of sulphur dioxide from iron sulphide materials, such as rabble furnaces, space roasters, and other types of distillation chambers, may be employed. Likewise, while my invention is particularly useful in connection with :the manufacture of sulphuric acid by the contact process, particularly in view of the increased conversion efficiency, it is to be understood that my invention is applicable broadly to the production of sulphur dioxide for any purpose where a higher sulphur dioxide to carbon dioxide ratio is desired or where coal brasses or other iron sulphide material containing carbonaceous matter is con sumed in sufficiently large quantities to warrant.

the recovery of the volatile hydrocarbons contained therein.

I claim:

1. In a process of producing sulphur dioxide by the combustion of carbonaceous iron sulphide material in which the capacity of the combustion apparatus is limited by the heat of combustion, the method of increasing the capacity of the combustion apparatus which comprises feeding the carbonaceous iron sulphide material into the combustion apparatus and passing the combustion gases in indirect heat exchange with the carbonaceous iron sulphide material being fed to the combustion apparatus under conditions such that the volatile hydrocarbons contained in the ironsulphide material are driven off prior to the introduction of the carbonaceous iron sulphide material into the combustion apparatus.

2. In the manufacturin of sulphuric acid from sulphur dioxide-containing gas obtained by the combustion of carbonaceous iron sulphide material the method of increasing the capacity of thecombustion apparatus and simultaneously of increasing the SOz/COz ratio of the sulphur dioxide-containing gas which comprises feeding the carbonaceous iron sulphide material into the combustion apparatus, passing the combustion gases in indirect heat exchange with the iron sulphide material being fed to the combustion apparatus under conditions such that the volatile hydrocarbons contained in the carbonaceous iron sulphide material are driven out prior to the introduction of the carbonaceous iron sulphide material into the combustion apparatus, and making sulphuric acid from said combustion gases.

ALBERT W. WAHLGREN. 

